Potassium easier in than sodium, cause polarization. Sodium-potassium pump, increase potassium, decreases sodium inside neuron. Action potential (neural firing) the neural impulse that passes along the axon and subsequently causes the release of chemicals from the terminal buttons: changes in electrical potential lead to action. Chemical signal from nearby neuron through dendrite tell: sensory neurons afferent neurons, detect information from the neuron fire/not. Signals arrive at dendrites by the thousands. Excitatory signals depolarize the cell membrane, increase likelihood neuron fire. Inhibitory signals hyperpolarize cell, decrease likelihood neuron will fire. If total excitatory signal received surpass receiving neuron"s threshold, action potential generated: excitatory & inhibitory signal sum = positive voltage change exceeding neuron"s firing threshold, action potential generated. Electrical charge inside cell starts slightly negative, becomes positives, fires and allows more positive ions inside, natural restoration to slightly negative physical world and pass that information along to the brain. Afferent neurons carry information to the brain.